Psoriasis is a chronic skin disease caused by cell proliferation in the basal layer of the epidermis which results in severe physical and psychological effects. The disease is characterized by circumscribed red patches covered with white scales. Photochemotheraphy is considered as one of the most promising advances in dermatologic therapy in the last ten years.
Photochemotherapy combines the use of chemicals and electromagnetic radiation to treat various skin disorders. There are a large number of reports which show the effectiveness of treating psoriasis with a photosensitizing reagent Psoralen, which is orally administered or applied topically to the skin, and with ultraviolet radiation with a wave length range between 320 and 400 nm, a method also known as PUVA. The methoxypsoralen generally used as the reagent, is one of several naturally occurring photoactive furocoumarin compounds found in plants such as clove, dill, lemon, parsley, etc. and has been evaluated extensively for the chemotherapy of psoriasis.
As known, the ultraviolet spectrum is subdivided into three main regions:
UVA, considered as long wave, with a spectrum in the range of 320-400 nm;
UVB, considered a middle wave, with a spectrum in the range of 290-320 nm, known as a sunburn region; and
UVC, considered a shortwave, with a spectrum in the range of 100-290 nm, known as a germicidal region.
Since metoxypsoralen reaches a maximum absorptive spectra at the wavelength of 325 nm,only the longwave ultraviolet light (UVA) was found to be useful as the light source. Also, UVA is less erythrogenic to normal skin than the UVB band, so that there is a lower risk of sunburn when UVA radiation is used. The methoxypsoralen serves also to make the skin more sensitive to the UVA radiation.
In contrast to the UVA treatment, known also as photochemotherapeutic method, there is the UVB treatment, known also as phototherapeutic method, in which only the therapeutic effects of UV radiation are used without the additional use of any chemical reagents. Generally, for this method the devices used as ultraviolet radiation are selected from light sources which contain UV emitting fluorescent lamps (a type of low pressure radiation devices), mercury high pressure radiation devices, Xenon radiation devices or mercury high pressure radiation devices doped with metal halides.
The shortwave radiation below 315 nm is suppressed by filters. There are known some UV fluorescent lamps in which the UV-B (under 320 nm) proportion is only a very low percentage whilst the UV-A proportion (over 320 nm) is very high. All the known devices are using suitable filters in order to suppress the undesired ultraviolet radiation. The literature is quite abundant with patents describing various devices with particular filters which are claiming to obtain the desired goal, i.e. a maximum UVA radiation to combat this disease.
Patients with severe psoriasis were faced with a choice between hospitalization and long-term ingestion of patent drugs that pose significant and potentially fatal complications. Accordingly,the approach of ambulatory psorlasis treatment became more and more considered as a most useful tool.
According to U.S. Pat. No. 4,712,014 the radiation lamp unit comprises a plurality of concave reflectors and light-orange radiation lamps and two UV lamp units which are arranged symmetrically to the center axis and in front to the focal point area of the light-orange radiation.
According to U.S. Pat. No.4,558,700 a UVB device useful for phototherapy of psoriasis is described. The device is characterized by its capability to correlate the radiation dose to the erythema threshold dose as a function of the radiation intensity of the wave length range of the ultraviolet resulted from an edge filter. The edge filter is made from an organic material such as polymethylmethacrylate,polyethylene terephthalate or polyvinyl chloride.
According to a very recent U.S. Pat. No. 4,909,254 a method for the phototherapy of skin wounds is described, using ultraviolet light from which the UVB component is substantially removed so that the wound is irradiated with UVC--having a wavelength of 200 to 280 nm--and UVA. The device used, comprises a high-pressure mercury-vapor gas-discharge lamp with a quartz envelope and a special construction of a selective UV-filter. The UV-filter comprises at least 2 layers and preferably up to 21 layers of dielectric materials which are non-absorbing in the UV region and which have different refractive indexes. Among the suitable materials to be used as filters there are mentioned: hafnium oxide, magnesium oxide, ytrium oxide, aluminum oxide and silicon dioxide.
Among the disadvantages of the known devices used phototherapy there should be mentioned their robust construction and only a partial effect which they produce against psoriasis, as well as their carcinogenic effect.
It is an object of the present invention to provide a simple method to be used against psoriasis. It is another object of the present invention to provide a simple device to be used for the ambulatory psoriasis treatment.
It is yet another object of the present invention to provide a simple device which overcomes the disadvantages inherent with known photo-chemotherapy, whereby the other beneficial properties of UV radiation can be utilized without the unnecessary damages and carcinogenic problems inherent with UVB radiation which is substantially completely eliminated.